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Patent Issued for Semiconductor Module with Electrical Switching Elements

August 20, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Hayashi, Yuji (Kasugai, JP); Handa, Yuuichi (Anjo, JP), filed on April 14, 2011, was published online on August 5, 2014.

The patent's assignee for patent number 8796816 is Denso Corporation (Kariya, JP).

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to a semiconductor module provided with electronic components, and in particular, to a semiconductor module provided with switching elements which serve as electronic components.

"There have been known power conversion apparatuses mounted in vehicles. Such apparatuses include apparatuses described by Japanese Patent Laid-open Publication Nos. 2000-333476 and 2008-136333.

"The power conversion apparatus described in these publications has a configuration shown in FIG. 1. Practically, as shown, a power conversion apparatus 90 has a semiconductor module 900 including switching semiconductors 82 and a smoothing capacitor 94 electrically connected to both positive and negative sides of a DC power supply. This power conversion apparatus 90 is used to, for example, convert DC power of a DC power supply 91 to AC power.

"Each of the switching semiconductors 92 has a switching element 95 which is for example an IGBT and a freewheel diode 96. Each switching element 95 has a gate terminal 95g connected to a not-shown control circuit board. This control circuit board controls on/off switching operations of the switching element 95. This control makes it possible to convert, to AC voltage, DC voltage applied between the positive-electrode terminal 98 of the high-potential side switching semiconductor 92H and the negative-electrode terminal 99 of the low-potential side switching semiconductor 92L, and to output the converted AC voltage from an AC output terminal 97.

"However, the foregoing conventional semiconductor module 900 generates a surge voltage when each switching element 95 is switched on/off. Hence, to resist this surge voltage, each switching element 95 should have a high withstanding voltage. This results in a rise in manufacturing cost of the power conversion apparatus 90.

"Meanwhile, there is known a technique of electrically parallel connecting a snubber capacitor to the switching element. This connection absorbs a surge generated by switching the switching element. However, a conventional semiconductor module has a snubber capacitor wire-bonded, so that the wire has a large amount of parasitic inductance L. This will cause a higher surge voltage (V=-Ldi/dt). As a result, the effect given by the snubber capacitor is insufficient."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "Hence, from the foregoing, it is desired to provide a semiconductor module which is able to reduce a surge caused in response to on/off switching operations of the switching element.

"In order to achieve the above object, the semiconductor module according to the present disclosure has, as ones of its fundamental components, a plurality of lead frames; switching elements electrically connected to the lead frames respectively; electronic components electrically connected to the switching elements; and a sealing member that seals at least part of the lead frames, the switching elements, and the electronic components, wherein the electronic components are mounted on primary surfaces of the lead frames.

"Hence, since the electronic components connected to the switching elements are mounted on the primary surfaces of the lead frames, inductance between the electronic components and connection parts of the lead frames can be lowered. If the electronic components are connected with wire bonding, the wires are apt to have parasitic inductance. However, in the present disclosure, without using wires, electronic components are directly mounted on the primary surfaces of the lead frames. Hence, the inductance can be lowered, so that surges (V=-Ldi/dt) caused in switching on and off the switching elements can also be suppressed and lowered.

"It is preferred that, in the foregoing semiconductor device, the electronic components have a pair of connection terminals, and one of connection terminals composing the pair of connection terminals and a corresponding one of the switching elements are arranged on the same lead frame.

"Hence, thanks to the foregoing configuration, compared with a configuration where the switching elements and the electronic components mounted on different lead frames and connected by wires or others, it is possible to reduce further the inductance between the switching element(s) and the electronic component(s). Surges caused in the operations of the switching elements can be lowered more.

"It is also preferred that the electronic components have a pair of connection terminals, the electronic components are connected between the two lead frames, and the pair of connection terminals are arranged, terminal by terminal, on the primary surfaces of the lead frames, respectively, which are different from each other.

"In this case, thanks to the foregoing configurations, inductance between the one lead frame and the electronic component(s) can be reduced, and the other lead frame and the electronic component(s) can be reduced. That is, inductance caused between the two lead frames can be reduced, whereby surges caused in the operations of the switching elements can be lowered more.

"Preferably, the semiconductor module comprises relaying lead frames positionally separated from the lead frames, wherein the electronic components have a pair of connection terminals, one terminal of the paired connection terminals is mounted on a corresponding one of primary surfaces of the relaying lead frames, and the other connection terminal is mounted on a corresponding one of the primary surfaces of the lead frames.

"In this case, the primary surfaces of the relaying lead frames and lead frames are used for arrangement of the electronic components, so that it is possible to reduce not only inductance between the relaying lead frame(s) and the electronic component(s) but also inductance between the lead frame(s) and the electronic component(s). This means that inductance caused between the lead frame(s) and the relaying lead frame(s) can be reduced, leading to lowering surges from the switching elements in a more reliable manner.

"Still preferably, the electronic components composed of a plurality of electronic components are connected in series via the relaying lead frames and two lead frames of the lead frames are electrically connected by both the plurality of electronic components and the relaying lead frames, the two lead frames being positionally separated from each other.

"In this serial connection of the plural electronic components, in cases where capacitors and resistors are used as the electronic components and one of those components is short-circuited, the normal operation of the module can be maintained as long as the other components are operating normally. This will raise reliability of the semiconductor module.

"Additionally, the foregoing configuration allows the plural electronic components and relaying lead frames to electrically connect the two lead frames, with no use of wires and leads. Accordingly, the amount of inductance between the lead frames can be reduced, lowering surges caused in switching on and off the switching elements.

"It is also preferred that the electronic components are either snubber capacitors or line bypass capacitors, the snubber capacitors being electrically connected parallely with the switching elements respectively to absorb surges caused when the switching elements are switched on and off, the line bypass capacitors being electrically connected between the switching elements and a ground terminal to absorb common mode noise caused when the switching elements are switched on and off.

"When the snubber capacitors serving as the electronic components are employed, surges from the switching elements can be absorbed. This means that switching elements having lower withstanding voltages can be used, reducing the manufacturing cost of the power conversion apparatus. Mounting the snubber capacitors on the primary surfaces of the lead frames reduces the amount of impedance between the lead frame and the snubber capacitor. A reduction in this impedance makes it easier that the current flows through the snubber capacitor when the switching element is made to switch at higher rate. Hence, soft switching can be performed easily and switching loss can be reduced compared to the conventional devices.

"Meanwhile, if the line bypass capacitors serving as the electronic components are employed, it is possible to reduce common mode noise leaking outside from the ground terminals via the stray capacitance of the semiconductor module. Additionally, incorporating the line bypass capacitors into the semiconductor module, the electronic circuit of this module can be made more compact, compared with not being incorporated, being improved in productivity of the semiconductor module. Still additionally, by locating the capacitors, which absorb the common mode noise, closer to the switching elements generating noise, the area of a loop through which the common mode noise flows can be reduced, leading in a reduction in emission of electromagnetic waves.

"It is also preferred that each of the snubber capacitors and the line bypass capacitors is a chip capacitor having connection terminals bonded to corresponding ones of the primary surfaces of the lead frames by soldering, welding, or using conductive adhesive.

"This configuration is helpful for further reducing inductance at portions connecting the snubber capacitor and the lead frame. If the snubber capacitor is realized by a capacitor having a lead wire, the lead wire may easily have a large amount of parasitic inductance L. In such a case, it is frequent that a surge (V=-Ldi/dt) becomes larger and switching loss becomes large as well. In contrast, chip capacitors soldered or bonded by other means are employed as the snubber capacitors and the line bypass capacitors, so that the snubber and line bypass capacitors can be connected to the lead frames without using lead wire. Thanks to this connection, the parasitic inductance between the capacitor(s) and the lead frame(s) is difficult to increase, leading to reduction in both surges from the switching elements and switching loss.

"Further, it is preferred that, of the switching elements, mutually serially connected two switching elements and, of the snubber capacitors, two snubber capacitors connected to the two switching elements respectively are grouped as one unit of switching element groups, wherein the one unit or plural units of the switching element groups are united for being sealed by the sealing member.

"Hence, compared to sealing switching elements one by one, the switching elements can be consolidated by the foregoing unified sealing manner, easily making an electronic circuit, thereby making the electronic circuit more compact and improving the productivity of the module.

"Preferably, the plural units of the switching element groups are connected parallely with each other and united with each other.

"This configuration results in an easier formation of electronic circuits by using the semiconductor module. For example, if two switching element groups are connected parallely with each other for unification, the semiconductor module can be used as a DC-DC converter. If there switching element groups are connected parallely to each other for unification, the semiconductor module can be used as an inverter.

"Still preferably, the switching element groups include two units of the switching element groups having four switching elements included in the switching elements, the four switching elements being located at positions virtually corresponding to apexes of a quadrangle when viewed along a line normal to the primary surfaces of the lead frames.

"Hence, this allows four switching elements to be located closer to each other. Inductance caused between these four switching elements can be reduced easily. Additionally, compared with arrangement of four switching elements along a linear line, the semiconductor module can be made more compact."

For additional information on this patent, see: Hayashi, Yuji; Handa, Yuuichi. Semiconductor Module with Electrical Switching Elements. U.S. Patent Number 8796816, filed April 14, 2011, and published online on August 5, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8796816.PN.&OS=PN/8796816RS=PN/8796816

Keywords for this news article include: Circuit Board, Semiconductor, Denso Corporation, Electronic Components.

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Source: Electronics Newsweekly


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